These days you can fly to far corners of the world and eat pretty much the same food you can get back home. There's pizza in China and sushi in Ethiopia.

A new scientific study shows that something similar is true of the crops that farmers grow. Increasingly, there's a standard global diet, and the human race is depending more and more on a handful of major crops for much of its food.

At the same time, all over the world, people are eating a bigger variety of foods. But until now, no one had crunched the numbers to see whether global diets were overall getting less — or more — diverse.

"We wanted to know, really, how many crops feed the world, and what's happening with them," says Colin Khoury, a visiting researcher at the International Center for Tropical Agriculture, or CIAT, in Cali, Colombia.

Khoury and his collaborators went through 50 years of data collected by the United Nations' Food and Agriculture Organization. And they uncovered two big trends.

In parts of Asia, such as China, rice is a declining portion of the average person's diet as they add other foods that are now more available. In the U.S., meanwhile, people are eating more imported foods, like mangoes and coconut water.

But here's the second discovery: Those bigger menus of food also are getting more and more similar to each other, from Nanjing to Nairobi. Everybody is relying more and more heavily on a few dozen global megafoods.

Many of those foods are part of what you'd call a standard Western diet, including wheat, potatoes and dairy. But other megacrops come from the tropics, such as palm oil. "It's grown on a large scale in Malaysia and Indonesia, but it's become a global commodity in diets essentially everywhere," says Khoury.

Smaller crops, meanwhile, are getting pushed aside. Sorghum and millet, for instance, are grown quite widely around the world, but they're losing out to corn and soybeans. Other small crops that you only find in certain areas could disappear altogether.

"In the Andes, aside from the potato, most of the rest of the traditional roots and tubers, crops like oca and maca, are declining in the amount of production and the amount of consumption," says Khoury.

A lot of things are driving this trend, he says. There's a rise in international trade, but also "people moving to cities, having more access to supermarkets, to fast food, having less time to cook, not having gardens."

The trend toward greater dependence on fewer crops continues, Khoury says. And so do the risks. It's dangerous to depend on just a few crops, because any one of them could be hit by some disaster, such as disease.

But governments and international organizations can still help to safeguard diversity in food sources. They can act to preserve the many genetic varieties of megacrops that still exist, and also preserve and encourage cultivation of minor crops, he says.

Rachel Laudan, a historian at the University of Texas and author of Cuisine and Empire: Cooking in World History, says it's important to remember that what drives the rise and fall of crops is demand for them after they've been transformed into something mouth-watering. "They're only interesting if they've been processed in some way," she says.

Think of all the things people do with wheat, she says. "You can get bread. You can get flatbread. You can get cakes. You can get pie. You can get beer!"

That's what turned wheat into a megacrop. Root crops, by contrast, were difficult to store, transport or process into interesting foods.

We could still turn some of these minor crops into attractive foods if there's enough interest in them, she says. In fact, interest may be reviving.

Consumers in the U.S. and Europe are snapping up little-known tropical fruits and so-called ancient grains, like farro and quinoa. Perhaps some of those minor crops can get their own spot on the global menu.

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Transcript

(SOUNDBITE OF MUSIC)

LINDA WERTHEIMER, HOST:

Travel to another country and you may be surprised to learn that more and more, you can find your favorite food, no matter where you are. There's pizza in China and sushi in Scotland.

And just as the menu looks very much the same across the globe, a new study shows that the world's farmers are growing an increasingly similar basket of crops.

NPR's Dan Charles reports.

DAN CHARLES, BYLINE: There's a slightly scary fact about our global food system. We humans depend on just a handful of crops for a lot of the food we eat. It's scary because any one of those crops could be hit by some disaster, like disease.

COLIN KHOURY: And we wanted to know, really, how many crops feed the world and what's happening with them.

CHARLES: That's Colin Khoury, a researcher at the International Center for Tropical Agriculture in Cali, Colombia. Khoury and some other scientists in Europe and the U.S. went through 50 years of data collected by the U.N.'s Food and Agriculture Organization.

They published their findings this week in the Proceedings of the National Academy of Sciences. Khoury says the numbers revealed two big trends. Here's the first.

CHARLES: Think of countries in Asia like China, where people traditionally ate lots of rice. These days, in those countries, rice is a declining portion of the average person's diet. In the U.S. meanwhile, people are eating more mangoes. All over the world, in fact, people are eating a bigger variety of foods.

But here's the second discovery. Those bigger menus of food also are getting more and more similar to each other, from Nanjing to Nairobi. Everybody is relying more and more heavily on a few dozen global mega-foods.

Many of those foods are part of what you'd call a standard Western diet, Khoury says - wheat, potatoes, dairy. But others come from the tropics, like palm oil.

KHOURY: It's grown in large scale in Malaysia and Indonesia and it's become a global commodity in diets, essentially everywhere.

CHARLES: Smaller crops are getting pushed aside. Sorghum and millet, for instance, are grown quite widely around the world but they're losing out to corn and soybeans. Other small crops that you only find in certain areas could disappear altogether.

KHOURY: Like in the Andes, aside from the potato, most of the rest of the traditional roots and tubers, crops like oca and maca are declining in the amount of production and the amount of consumption

KHOURY: People moving to the cities, having more access to supermarkets, to fast food; having less time to cook and not having gardens.

CHARLES: Khoury says the bottom line is what people feared is true. We are more and more dependent on just a few dozen big crops. That trend probably can't be stopped, he says. But governments and international organizations can help to safeguard diversity in our food sources. They can preserve the many different genetic varieties of mega-crops and promote minor crops.

Rachel Laudan, a historian at the University of Texas and author of the book "Cuisine and Empire," says what drives the rise and fall of crops though, is demand for them after they've been transformed into something mouth-watering.

RACHEL LAUDAN: They're only interesting once they've been processed in some way.

CHARLES: Think of all the things people do with wheat.

LAUDAN: You can get bread, flatbread. You can get porridge. You can get cake, pie. You can get beer.

CHARLES: That's turned wheat into a mega-crop. Root and tubers, by contrast, were hard to store, or transport or process into interesting foods. We can turn some of these crops into attractive food, she says, if there's enough interest. And there now may be. Consumers in the U.S. and Europe are snapping up little-known tropical fruits and so-called, ancient grains. Maybe some of those minor crops can now find their spot on the global menu.